Which instrument requires a primary and secondary monochromator for its operation?

The correct answer is that the instrument requiring both a primary and secondary monochromator for its operation is the fluorometer.

Fluorometers are specifically designed to measure the intensity of fluorescent light emitted by a sample when it is excited by a light source, usually UV light. The presence of both primary and secondary monochromators is essential in a fluorometer to ensure that the excitation source is precisely filtered and that the emitted fluorescence is accurately observed. The primary monochromator selects the wavelength of light used to excite the sample, while the secondary monochromator allows for the selection of the specific wavelength of the emitted light to be measured. This dual-filtering system enhances the instrument's sensitivity and specificity, allowing for more precise measurements in quantitative fluorescent assays.

In contrast, a spectrophotometer typically uses a single monochromator to isolate the light for either absorption or transmission measurements across a wide range of wavelengths, which does not demand the two-stage filtering that fluorometers require. An atomic absorption spectrophotometer also usually relies on a single monochromator specifically designed for absorbing elements. A nephelometer measures scattered light and generally does not utilize monochromators, focusing instead on the intensity of the scattered light at different angles without the need for